An acoustic logging tool may include one or more acoustic sources and a set of receivers that are spaced apart from each other. Acoustic signals may be transmitted by the acoustic sources and received at the receivers as the tool is drawn through a borehole. Thus, the acoustic signal from each source may travel through the formation adjacent the borehole to the receiver array, such that arrival times and other characteristics of the receiver response may be recorded. Received signals may include compressional wave (P-wave), shear wave (S-wave), and Stoneley waves. Received signal data may be processed to find formation characteristics, including slowness (the inverse of acoustic speed), from which pore pressure, porosity, and other formation property determinations can be made.
Traditional multipole acoustic tools use a set of sources that are as close to identical to each other as possible for generating various wave modes. Generally speaking, this practice is intended to reduce source-imbalance induced mode contamination that can operate to reduce array coherency of a particular desired mode. However, the usefulness of the measurements obtained may be reduced due to bandwidth limitations imposed by a matched set of sources.